Is this mastering physics problem incorrect?

[Second_addition]

Homework Statement

[/B]
This is the Diagram-The figure shows the circular wave fronts emitted by two wave sources.
https://session.masteringphysics.com/problemAsset/1383558/3/21.EX26.jpg
part B is the one with trouble it asks "Make a table with rows labeled P, Q, and R and columns labeled r1, r2, Δr, and C/D. Fill in the table for points P, Q, and R, giving the distances as multiples of λ and indicating, with a C or a D, whether the interference at that point is constructive or destructive."
The given wave lengths to fill in the charts blank spaces are (1/2)λ,,,λ,,,(3/2)λ,,,2λ,,,(5/2)λ,,,(3)λ and then c for constructive and D for destructive for the last column.

Homework Equations

abs(r1-r2)=Δr and for C/D and Δr that is a natural number is C all decimal numbers are Destructive //sorry don't know how to put that into more mathematical format//
3. The Attempt at a Solution [/B]
the chart should look like- Unfortunately their is no 3.5 fraction 7/2 is missing^
r1 r2 Δr D/C
P 2λ 3.5λ 1.5λ D
Q 3λ 2λ 1λ C
R 2.5λ 3.5λ 1λ C

 

[TSny]

Hello and welcome to PF!

To my eyes, the first wavefront surrounding source 1 is a full wavelength from source 1. But the first wavefront surrounding source 2 is not a full wavelength from source 2. Could it be that the two sources are not in phase?

 

[Second_addition]

Hello and welcome to PF!

To my eyes, the first wavefront surrounding source 1 is a full wavelength from source 1. But the first wavefront surrounding source 2 is not a full wavelength from source 2. Could it be that the two sources are not in phase?

Yes your right so instead of 3.5 it would be 3 making it work thank you